Electrophoretic borating of copper wire



May 26, 1953 R. E. PALMATEER 7 2,640,024

ELECTROPHORETIC BORATING OF COPPER WIRE Filed Nov. 2. 1948 EA. 6.92 V. 2$92 1 ,INVENTOR. Russelfi. fizz/mates MKw-ZWAA Attorney Patented May 26,1953 ELECTROPHORETIC BORATING OF COPPER WIRE Russell E. Palmateer,Emporium, Pa., assignor to .Sylvania Electric Products Inc., acorporation of Massachusetts Application November 2, 1948, Serial No.57,994

2 Claims. 1

This invention relates to a method of coating wire; more particularly itrelates to a method of coating wire with a vitreous material by anelectrophoretic process.

In accordance with prior art practices for coating wire with a vitreousmaterial such as borates or soft glass materials, the vitreous formingmaterial has normally been applied in a purely mechanical manner bydipping or brushing the material onto the surface of the wire. Forexample, in the borating of copper or copper clad wire as has heretoforebeen the custom, the wire is first heated in an air furnace to removecontamination and more particularly to oxidize the copper surface sincethis oxide surface appears to be quite necessary if a satisfactoryborate coating is to be applied. The thickness of this oxide and itsappearance is, therefore, quite critical. Following this, the borate isapplied in a thin coating by painting on or by dipping the wire into awater suspension or solution of the borate maintained at the properconsistency to deposit the most desirable amount of solid material,after which it is dried and heated at a critical temperature to fuseflow the coated material into a skin. In coating wire such as Dumetwhich is a copper clad nickel iron wire used for glass sealing in theelectronic industry, a continuous process has been developed wherein thewire is moved successively through these stages and finally aftersuiiicient cooling is wound on spools. Such a process isdiagrammatically illustrated in Patent No. 2,316,984.

Although this process has been used commercially for some considerabletime, it is understandably not completely satisfactory since it issomewhat dependent upon pre-oxidation of the wire which step needs to bekept under careful control at all times if a satisfactory product is tobe obtained. Furthermore, the presence of the water along with theborate also leads to the formation of bubbles in the surface. These areattributable to the hydrated salts that are used thus producing finishedproducts whose coating can by no means be considered smooth and even.Furthermore it is at times difficult to control the coating thickness.Since this mechanical coating method dependsin large part upon theheating of the wire, before the dipping operation in order to form asuitable oxide finish, it was not considered the best manner ofapplication on an annealed wire used for such purposes.

It is an object of this invention to provide an improved method ofapplying a vitreous coating to metals which is adapted to produce aneven uniform coating having no bubbles in the finished surfacesuch asthose normally encountered due to the use of hydrated salts.

It is a further object of this invention to provide a method of applyinga vitreous coating which will require no previous oxidation of themetal. I

It is a still further object of this invention to provide a method ofapplying a vitreous coating in a manner which will not interfere withthe annealed condition of the base metal to be coated.

In accordance with this invention these and other advantages which areincidental to its application, can be attained by electrophoreticallycoating the wire from a suspension ,of vitrifiable material and metaloxides.

In the accompanying drawing which illustrates the preferred method ofthis invention:

Fig. 1 is a schematic drawing showing the preferred method and apparatusembodying features of this invention;

Fig. 2 is a schematic drawing showing a. modified version of the methodand apparatus shown in Fig. 1.

In accordance with this invention, it has been found that metal can becoated with a vitreous material in a manner requiring no preoxidation toobtain even uniform coatings having no bubbles in the finished surfaceif the material is coated electrophoretically from a bath containing asuspension of the vitrifiable frit material in intimate mixture with anoxide of the material to be covered.

Electrophoretic methods of coating metals with non-conductors are ofcourse quite well known to the art.

However, it has not heretofore been considered possible to apply avitreous coating to such metals without previously oxidizing the metalif a good adherent coating was desired.

In accordance with the method of this invention however, it becomesunnecessary to oxidize the surface of the wire to produce good adherentcoatings. Furthermore it has been found that the presence of the oxideof the base metal in the frit suspension tends to increase the rate atwhich the vitrifiable material can be applied to the base metal byelectrophoresis.

In the case of copper wire, for example, it was found that wire whichcould only be borated electrophoretically at the slow rate of seven feetper minute could be borated at the rate of 16 feet per minute or morethan twice as fast if copper oxide were present in the bOratingsuspension.

In accordance with preferred embodiments of this invention in whichclean copper wire is borated without first applying an oxide film to thewire, the spool H] of the annealed wire as shown in Fig. 1 feeds thewire l2 over a guide pulley l4 electrically grounded by line [6. Thewire 12 passing downwardly into .a coating tbath around ta-guide pulleyat the bottom of it, upwardly out of the bath past a cathode connectedto a power line 20. As the wire leaves the coating bath it passesthrough a, furnace .30 which .is operated at a temperature of about 900degrees C. or above to fuse the borate coating. The wire thereuponpasses up to a winding ispoolrn which is located a sufiicientdistanceiabove the furnace that the borate will solidify before itreaches the winding spool or pulley 32. .-.shown.in.l .ig..2, a dryer 40may be placed between the coating bath and the furnace for the purposeof ievaporating the solvents before the wire reaches the furnace .30 ifso desired. FI-his dryer :norm'ally operates at 150-.20.0'degrees- C..inpreferred-cases.

In accordance with preferred embodiments of this invention, .the coatingbath -is;made -.up of a suspension of the vitrifiable material in finelydivided form and powdered metallic oxide .ina suspension of the waterfree organic medium which is not hydrophi1ic.and.does7not have atendency to absorb moisture. .Agpreferred formula forthe boratingzof@Dumet wire 21S, for example, one which-contains 1 grams :of sodiumborate (anhydrous), .5 gram OfCUZQ,/20.0 CCS. of amyl acetate .and 100cos. of lacquer :containing approximately .9 .gram of anhydrous 1000second nitrocellulose per .100 .ccs. of .-hi gh purity amyl acetate.This solution .to give -.the-best.results:is ball-milled vlover night,that is, .for a period :of about 12 .hours after which .the suspension:gives best results after having been diluted with .two litres ofamylacetate. Whensoperating with'this solution, it has been foundthat-.the;heat +required for boratingtotakeplace is 1900degrees C. Therate of coating .isabout .16 -feet per minute. This permits the wire tobe heated at 900 degreesCtfor 4- .seconds and allows .it :to :be cooledin air :for 320 seconds. The process requires the [use of :voltages ofless than 100 volts .during which the borate moves and adheres to ithewire :at low electrical potential. For .the eoatingrof.0162.:Dumet=wire, the voltage required .at the beginning iiszabout r60volts which is gradually increased to :90 volts when 10,000 feet of wirehave ;.passed through the suspension.

method has been found .to 'be. successful and satisfactory .for,.pr.oduction 'of even coatings with other vitreous materials besides:borates namely with glass Hit of types G12, '61 -borax glass. Thecomposition for -G12 glass .-is approximately .as follows: 5.6.7 iof.SiQz, 3.32% :of Na2CO3, 7.9% of mo, 06% of Ca, 28.4% :EOf PbO, 1.3% ofR203. .Gl .glass has the Jollowing approximate compositions .of: .2016%P1), 62.2% or SiOz, 6.84% .of .NazCea, 6.45% of .KzQ :and 1.05% of R203.There is, of.course,--nothing.novel in thefact thatnon-conductingsmaterials:suchgas glass frit, aluminum oxide, silica,any-of .theanhydrous sillcatesor anyother yitrifiablemateria-l can bedeposited electrophoretically. Thenovel feature in the composition hasvin the inclusion of a metallic .oxide which .permits -.the .omission ofa preoxidation treatment .as welhas means -.to speed up theelectrophoresis .while ,yet .obtaining satisfactorygood adherentcoatings .of .the yitreous material.

Although copper oxide 'isperhaps the mostuse- 4 ful of the metallicaddition agents to the suspension in view of the large use of copperclad wire in making glass to metal seals, other metallic oxides can alsobe used to advantage particularly when the base material is to be coateda metal other than copper. Examples of *suchoxides are chromicoxide'ICriOa,;tungstic ox- -ide W Oa cobaltieoxide,iron oxideand-aluminum oxide.

Other examples of preferred bath formulations in whichsuch oxides areused are, for ex- ;ample, as follows:

I. 25 gms. of #775 Pyrex glass (powdered) '25znl.:amyljacetate 5 ml. .of.lacquer containing approximately 3133 g. of anhydrous 60-80 secondnitrocelzlulose per ml. of high purity amyl acetate .5 gm.tungstic oxide-.(WO3) 1 gm. sodium borate H. 200 gmsmpulverized G-l glass 250 m1. amylacetate 50ml. of lacquer (same as in I) 10 gins. green anhydrouschromicoxideyCmO:

The :amount of oxide activator added .to the electrophoretic bath -may,-.of course, .vary over wide limits. Increasin the amountof the oxide inthe .bathain relation .to .the .total solid material tends .toincreasethespeed at'which the'electrophoretic deposition willtake place.However, if toorgreatainountsaroused, there willbea tendencyfointhedeposit to become'non-adherent and flaky. For this reason,itehasbeenfoundpreferable when depositin from baths -.containing"cuprous oxide, for example, .to limit the cuprous oxide to..04% vto.08%of the .total solid-material. On the other hand, the amount of .tungsticoxide which maybe added .without deleteriously affecting .the coating isas much .as 2% of the total solids. 'With .chromic oxide, themetal-oxidecan be further increased to as much as .5% without deleteriouslyaffecting .the adhesive properties of .the coating.

It is, .of .course, understood that while :the process of .thisinvention .makes vit possible to coat either single or composite :metalswithout previously oxidizing the metal surface to be coated, the factthat such metal surface may have controlled oxidation is notdetrimentaland will not have a deleterious .effect on the finishedproduct.

"While the above description and drawings submitted herewith disclosepreferred :and practical embodiments .of .the coating method of thisinvention, .it .will vbe understood by those skilledin the .art that thespecific -.details shown and describedare .by way of.il1ustration and.are not to be construed aslimiting .the scope of the invention.

What is claimed is:

'1. An electrophoretic bath .for oxidized copper wire with .a lboratecoating preliminary to using it in making a seal .to glass consistingessentially of .a suspension of a mixture :of sodium "borate andpowdered cuprous oxide in an anhydrous non-hydrophilic organic liquid-of'low electrical conductivity.

.2. In the .eleotrophoretic method of coating unoxidized copper wirewith :a borate coating preliminary to using .it .in making a seal :toglass, the steps .comprising passing the copper wire through asuspension -.of a mixture :con sisting essentially of sodium'borate .andpowdered coating .un-

cuprous oxide .in a non-aqueous, alone-hydro philic organic medium,maintaining an electric potential between said metal and a cathodethrough said suspension and thereby causing the mixture of ,sodiumborate and cuprous oxide to coat the copper wire, withdrawing the copperwire from the suspension and passing the coated copper wire through aheated area wherein the sodium borate is caused to flow evenly over thesurface of the copper wire.

RUSSELL E. PALMA'I'EER.

References Cited in the file 0! this patent UNITED STATES PATENTS NumberName Date Steenbeck et al Aug. 15, 1933 Ruben Sept. 10, 1940 Verwey eta1 June 8, 1943 Robinson et a1 June 3, 1947

2. IN THE ELECTROPHORETIC METHOD OF COATING UNOXIDIZED COPPER WIRE WITHA BORATE COATING PRELIMINARY TO USING IT IN MAKING A SEAL TO GLASS, THESTEPS COMPRISING PASSING THE COPPER WIRE THROUGH A SUSPENSION OF AMIXTURE CONSISTING ESSENTIALLY OF SODIUM BORATE AND POWDERED CUPROUSOXIDE IN A NON-AQUEOUS, NON-HYDROPHILIC ORGANIC MEDIUM, MAINTAINING ANELECTRIC POTENTIAL BETWEEN SAID METAL AND A CATHODE THROUGH SAIDSUSPENSION AND THEREBY CAUSING THE MIXTURE OF SODIUM BORATE AND CUPROUSOXIDE TO COAT THE COPPER WIRE, WITHDRAWING THE COPPER WIRE FROM THESUSPENSION AND PASSING THE COATED COPPER WIRE THROUGH A HEATED AREAWHEREIN THE SODIUM BORATE IS CAUSED TO FLOW EVENLY OVER THE SURFACE OFTHE COPPER WIRE.